Jointed concrete structures

ABSTRACT

Concrete is cast with a dummy joint sealed by a flexible waterstop embedded by keying formations into the concrete, by a method in which a crack is formed as the dummy joint, a crackinducing body, e.g., a piece of wood being fixed in position, e.g., by spring clips, opposite the center line of each waterstop. The invention also includes a novel assembly of a waterstop and a spring clip for holding the crack-inducing body.

Unite States Patent Hurst [451 Dec. 19, 1972 [541 JOINTED CONCRETE STRUCTURES 2,319,049, 5/1943 Fischer ..94 1a Inventor: J Hurst, e m ter Lon on 2,444,372 I- 6/1948 Robertson ..94/[8 S.W. l England [73] Assignee: W. R. Grace & Co., New York, Primary Examiner-Jacob L. Nackenoff N. Y. Attorney-C. Edward Parker 22] Filed: Nov. 14, 1969 [21] APPI. NOJ 58,752 [57] ABSTRACT Related U.-S. Application Data Division of Ser. No. 731,374, May 23, 1968, Pat. No. 3,578,733.

US. Cl ..94/17, 94/18 Int. Cl ..E01c 11/02 Field of Search ..94/17, 18; 52/396; 264/35 Concrete is cast with a dummy joint sealed by a fle xible waterstop embedded by keying formations into the concrete, by a method in which a crack is formed as the dummy joint, 21 crack-inducing body, e.g., a piece of wood being fixed in position, e.g'., by spring clips, opposite the center line of each waterstop. The inventioii also includes a novel assembly of a waterstop and a spring clip for holding the crack-inducing body.

4 Claims, 4 Drawing Figures PATENTED DEC 19 1912 SHEET 1 BF 2 PATENTED DEC 19 I972 SHEET 2 OF 2 '24 B u ll JOINTED CONCRETE STRUCTURES This application is a division of Ser. No. 731,374, filed May 23, 1968, now US. Pat. No. 3,578,733.

This invention relates to concrete structures.

When concrete dries out after pouring, it contracts, and unless special measures are taken to prevent this, cracks tend to develop randomly in the concrete. Such cracks are highly disadvantageous in that they allow water to percolate through the concrete, and this problem becomes more serious with the passage of time, since the expansion and contraction of the concrete induces fresh cracks and enlarges those already present. It has long been the practice to mitigate the seriousness of this problem by intentionally introducing a plane of weakness into the concrete, as a result of which the cracks develop along the plane of weakness and not elsewhere. The plane of weakness is conventionally introduced by forming a depression in 'the surface of the concrete, for example by means of a V-sh'aped batton placed against the formworkor a saw cut made in the surface of the concrete. The crack is then sealed by the application of a sealing compound to the depression. A difficulty that arises with such .dummy joints, as these induced cracks are known, is that they can only be sealed by the application of a sealing compound and such sealing is not effective against any substantial pressure of water, particularly when the water pressure tends to displace the sealing compound, and furthermore the sealing becomes markedly less effective with the passage of time. In addition, where reinforced concrete is used, the reinforcement is on the wet side of the sealing strip and is, therefore, liable to corrosion. Other methods of sealing dummy joints have been proposed but none is a practicable proposition. Thus the conventional method of sealing joints between separately poured masses of concrete, namely, by a strip of rubber or rubber-like material of dumbell cross-section, one half of which is embedded in each mass of concrete, is not applicable to dummy joints because it is impossible to place the waterstop accurately in the middle of the poured concrete in relation to the subsequently induced crack. As a result,'it has not hitherto been possible to use dummy joints in concrete structures below ground or in other places where a substantial water pressure is to be expected. Instead, since some form of joint is essential at regular intervals in a concrete structure, in order to ensure that expansion and contraction of the concrete is accommodated without the development of random cracking, it has been necessary to form expansion, contraction or construction joints; such joints, which are formed by adjacent and separately poured masses of concrete, can be effectively sealed, even against substantial water pressures, by means of waterstops. However the making of such joints is extremely time-consuming and expensive, since the first mass of concrete must be allowed to harden before the second mass can be poured and must of course be supported by formwork while it hardens. Where a long length of concrete is to be layed, it is usual to employ alternate bay construction,as illustrated in FIG. 2 of the accompanying drawings.

We have now surprisingly discovered that, contrary to the long established and accepted belief of those skilled in the art, it is possible, by making use of a novel waterstop assembly, to form a dummy joint in a concrete structure so that the joint is effectively sealed by a waterstop, even against substantial pressures of water, as in structures below ground. The method of the invention will be described chiefly by reference to joints running vertically through a generally horizontal structure, e.g. the base of a building; it is to be understood, however, that it is equally applicable to other dummyjoints, e.g. in walls.

Our British Specifications Nos. 1,008,81 l and 1,008,812 disclose a novel form of waterstop which is described for use in the cooling of a concrete joint formed by two adjacent and separately poured masses of concrete,i.e. an expansion, contraction or construction joint the said joint is sealed by a waterstop in the form of an extruded or molded section of rubber or other moisture and water-resistant flexible plastics material, the extruded or molded section comprising a strip-like body having at least one formation broadening out from its root for keying into concrete projecting laterally from the waterstop on each side of the center line thereof, the keying formations all projecting from the same face of the waterstop and being so placed that outside each of the keying formations nearest the center line of the waterstop there is a portion of the waterstop through which nails may be driven to secure the waterstop to shuttering; the said waterstop, which is referred to hereinafter as a waterstop as hereinbefore defined, is positioned with the keying formations of the waterstop embedded in the concrete whilst the outer face of the waterstop is not embedded in concrete, so that the joint falls between the two keying formations nearest the center line of the waterstop.

A waterstop as hereinbefore defined is illustrated, in perspective view, in FIG. 1 of the accompanying drawings.

The term keying formation broadening out from its root is used herein to include any formation which will key satisfactorily into concrete and is broader at some point more remote from the strip-like body than it is at another point closer to the strip-like body. For example the keying formation can be T-shaped or in the shape of an inverted truncated triangle. Generally, the keying formations will all be the same shape, but this is not necessary.

We have now discovered that by using a waterstop as hereinbefore defined in a particular water-stop assembly, it can be used to provide a waterstop across a dummy joint. This discovery is of great importance because it makes possible the pouring of much longer lengths of concrete than has hitherto been possible.

The method of the present invention comprises positioning a waterstop as hereinbefore defined flat on a base onto which concrete is to be cast, and/or securing the waterstop to shuttering, positioning a crack-inducing body within the space where the concrete is to be cast and opposite the center line of the waterstop, and casting concrete in a single pour which extends across the waterstop and crack-inducing body, so that the keying formations of the waterstop become embedded in the concrete, while the opposite face of the waterstop is not embedded, and a crack (which constitutes a dummy joint) is caused subsequently to form between the keying formations. Such a crack-inducing body can be a. projection integral with the waterstop, but it is much preferred to use a piece of wood or any other rigid or semirigid material which is secured in place after the waterstop has been positioned against the base or shuttering. In this way, a building contractor need only have available to him one type of waterstop, which is, however, used differently depending on the type of joint to be made (i.e. a dummy joint in accordance with the present invention or an expansion, construction or contraction joint in accordance with the invention of British Specifications Nos. 1,008,811 and 1,008,812 referred to above). It is particularly preferred to secure the crack-inducing body in place by means of clips of suitable material such as metal, e.g. spring clips, which are themselves secured to the waterstop at intervals along its length. Such clips are conveniently secured to lugs projecting from the face of the waterstop and formed integrally therewith; such clip-securing lugs preferably broaden out from their-roots (particularly when spring clips are used) and thus serve also as formations for keying into the concrete; particularly, when the clip-securing lugs broaden out from their roots, it is preferred that there should be a further key ing formation outboard of each of the clip-securing lugs, so as to eliminate any danger of the creation of a waterpath in the region of the clipsplt. is in any case preferred that the waterstop should have at least two pairs. of keying formations in order to ensure that the waterstop is fully secured to the concrete and to ensure an adequate water barrier. In addition to the clips securing the base of the crack-inducing body to the waterstop, the body can also be held in place in other ways, for example by clips or wires attached to the crack-inducing body and to reinforcing bars and/or to bars specially provided for this purpose which may or may not become embedded in the concrete.

The crack-inducing body may be secured so that it touches the center portion of the waterstop or so that it is separated therefrom, e.g. by a distance of 2.5 to 10, preferably to centimeters. Such separation is particularly desirable when the concrete contains reinforcement, which can then pass underneath the crackinducing means, as well as, of course, over the top of it. It is not generally convenient for reinforcement to pass through the crack-inducing means, though this possibility is not excluded from the present invention.

In addition to the crack-inducing body placed within the concrete, it is possible also further to weaken the concrete in the same plane by conventional means, by forming a depression in the surface of the concrete opposite to the waterstop. Such conventional means alone are not, however, sufficient to ensure that the induced crack will terminate within the waterstop, as is of course essential. The additional use of such conventional means is particularly desirable where a water barrier is required against water or moisture on both sides of the crack or where the appearance of the opposite face is important, because the depression can be filled in any suitable way. Thus a sealing compound is used when a water barrier is required against water or moisture on both sides of the crack, e.g. on roads and underground culverts.

The size of the waterstop to be employed and of the crack-inducing body will be to some extent dependent on the dimensions of the concrete structure and the water pressure to which the structure is likely to be exposed, as also will the distance between adjacent dummy joints where rnore than one is required. The

height of the crack-inducing body should generally be 1/2 to two-thirds the depth of the concrete and the distance between adjacent dummy joints 3 to 7.5 meters, preferably about 4.5 meters.

As with all waterstops, it is essentialtov provide a complete continuous barrier to water over the whole surface of the joint which is exposed to water or moisture pressure. The precise nature of the water barrier need not be the same over the whole surface of the joint (though this is usually desirable). A particular advantage of the novel waterstop assembly is that two or more waterstops can readily be joined together, if desired, to form a complete network. Thus where the waterstop has to change direction and runs in two planes inclined-to each other, e.g., the horizontal and vertical planes, it is a simple matter to achieve this by means of a suitable preformed junction piece, which (by reason of the material of whichthe waterstop is made) can readily be joined in situ to the main strips to form acontinuous waterproof run of waterstop. Alternatively the waterstop can simply be bent through the desired angle. Likewise where joints intersect, suitably shaped junction pieces (e.g., in the form of a T, X or Y) can readily I be employed. While the crack-inducing means will in general besomewhat more complicated in such situations,-in order to ensure formation of the dummy joint in the required position, this does not present any difficulty. Another particular advantage of the novel waterstop assembly is the case with which the waterstop can be secured in any desired position against shuttering (formwork) by driving nails (preferably double-headed nails) through the waterstop outside at least the innermost pair of keying formations; the waterstop preferably has a nailing flange outside any of the keying formations, through which flange the nails are driven.

In the accompanying drawings:

FIG. 1 is a perspective view of a short length of waterstop as described and illustrated in British Specifications 1,008,811 and 1,008,812;

FIGS. 2 and 3 are side views of concrete cast respectively by a known method and by the method of the invention; and

' FIG. 4 is a perspective view of a spring clip as shown in FIG. 3.

The waterstop of FIG. 1 has already been referred to above; it comprises a body portion 1, having keying formations 3 and 4 on each side of the center line, and a marginal portion 5 through which nails may be driven. The precise cross-sections of the keying formations may be varied from those shown.

FIG. 2 shows concrete being cast by alternate bay construction upon a base 2, which may be of concrete or compacted earth. Concrete has been cast in the bays 4, supported by temporary stop end shutters 6, which are held erect by supports 8. The bay 10 has not yet been cast. Beneath the junction of each bay is a waterstop 12(as shown in FIG. 1) to prevent entry of ground water.

In FIG. 3, the concrete 4 has been cast continuously without use of stop end shutters (except as may be needed at the end of a days pour). A crack-inducing piece of wood 14 is fixed by spring clips 16 to the inner keying formations of each waterstop 12. FIG. 4 shows a perspective view of a preferred form of the clip 16,

which may be fabricated from a single strip of ternpered metal, preferably steel. Two or more clips, depending on the length of the waterstop (i.e. the width of the concrete) are used for each waterstop. A nail may be passed through the wood 14 and through the hole shown in FIG. 4 at the top of the clip, to assist in retaining the wood in position. Tabs 21 embrace lugs or keying formations 3 on each side of the center line.

As an illustration of the advantage of the method of the invention, the following figures are provided. A piece of concrete 4.5 meters wide by 4.5 meters high by 300 meters long could be laid in about 70 working days by the prior method illustrated in Fig, 2, and in only about 40 working days by the method of the invention as shown in FIG. 3. (The precise times will vary depending on the nature of the concrete and other factors.)

point where said crack is to be induced, said strip having upstanding, spaced, longitudinally extending lugs projecting from one face of said strip, a spring clip having an upper pocket remote from said strip to receive a crack inducing member, said clip having outwardly diverging leg portions supported on said waterstop, each leg portion being provided with a hook-like tab embracing one of said lugs to hold said clip in position.

2. The assembly of claim 1 wherein said clip is fabricated from a single strip of tempered metal.

3. The assembly of claim 1 wherein said flexible strip material has an additional pair of upstanding, spaced, longitudinally extending lugs projecting from the same face of said strip, one each of said additional lugs being positioned outboard of said lugs embraced by said leg portions.

4. The assembly of claim 2 wherein said lugs are configured such that they broaden out from the point at which they join said flexible strip material and thereby serve to key. said waterstop into said concrete slab. 

1. An assembly for inducing a crack in a concrete slab, said assembly comprising a waterstop of resilient, flexible strip material adapted to be positioned on a surface against which the slab is to be poured and at the point where said crack is to be induced, said strip having upstanding, spaced, longitudinally extending lugs projecting from one face of said strip, a spring clip having an upPer pocket remote from said strip to receive a crack inducing member, said clip having outwardly diverging leg portions supported on said waterstop, each leg portion being provided with a hook-like tab embracing one of said lugs to hold said clip in position.
 2. The assembly of claim 1 wherein said clip is fabricated from a single strip of tempered metal.
 3. The assembly of claim 1 wherein said flexible strip material has an additional pair of upstanding, spaced, longitudinally extending lugs projecting from the same face of said strip, one each of said additional lugs being positioned outboard of said lugs embraced by said leg portions.
 4. The assembly of claim 2 wherein said lugs are configured such that they broaden out from the point at which they join said flexible strip material and thereby serve to key said waterstop into said concrete slab. 